How does sustained covert attention affect early visual processes? Whereas it is well established that transient, exogenous attention, enhances early vision, it is unknown whether sustained, endogenous attention affects early vision, and if so, how and to what degree. The proposed psychophysical studies will address this question by investigating: (a) whether sustained attention affects early vision (contrast sensitivity and spatial resolution) via the mechanism of signal enhancement, (b) the time course of sustained attention's effect on contrast sensitivity, (c) the phenomenological consequences of sustained attention on apparent contrast, and (d) the effect of both transient and sustained attention on the processing of 2nd order stimuli (non-Fourier; orientation-modulated noise). These experiments will shed light on our understanding of sustained attention and early visual processes that are well characterized both psychophysically and neurophysiologically. Moreover, these experiments will help bridge the gap between the psychophysical and neurophysiological research on attention; whereas most psychophysical studies deal with transient attention, virtually all neurophysiological studies deal with sustained attention. [unreadable] [unreadable]